Arrangement for suppressing idle current in radiotransmitters



May 31', 1927. 1,630,349

A. MEISSNER ARRANGEMENT FOR SUPPRESSING IDLE CURRENT'IN. RADIOTRANSMITTERS Filed April 6. 1925 INVENTOR ALEXANDER MEISSNER AT ORNEY Y Patented May 31,1927,

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ALEXANDER MEissNnR, or BERLIN,GERMANYQASSIGNOR To GEsELLsOHAFT (FUR nnAHT osnrnLEeRAPHIn ran. 1a., or BERLIN, GERMANY.

ARRANGEMENT non snrrnnssrne IDLE cunnnnr IN RADIOTRANSMITTERS.

' Application filed April c, 1925, Serial No. maze-and ineeim anyn i ilo, 1924.

My invention relates broadly to apparatus for modulatedwave transmission and more specifically to radio telephony transmitters. An object of the invention is to pr'ovidea radio telephony transmitter in which the 4 carrier wave issuppressed both when speech is being transmitted and when speech is not beingtransmitted.

Other objects will be apparent from the following specification and claims when considered with the accompanying drawing which diagrammatically illustrates the best embodiment of my invention known to me at the present time.

' When modulating highfrequency oscillations by acoustic oscillations, for the pur poses of telephony,-it is well known that in the transmitting station generally three fre- V known'manner to generate sustained osclllaquencies are produced. They arethe car rier wave, and the two sidexbands, one side bandhaving a frequency equal to the'carrier frequency plus speech frequency and the other side band having a frequency equal to the carrier frequency minus the speech frequency. The'carrier frequency, which alone is being radiated during the speech intervals, has been called the idle current. This current when not used for the transmission of modulating waves, is'often found to be of great disturbance, particularly so in telephony reception by superposition, that is, beat reception. On account of the presence of the carrier of high frequency, the entire frequency band required by the transmitter becomes furthermore unduly .wide. It has therefore been suggested to work with the carrier wave suppressed, and for this ohliect certain differential connections of senders have been proposed. It has been found, however, that. such arrangements are attended with various technical difficulties.

- Now, the present invention furnishes means of a simple nature whereby the nudesirable idle current can be removed from the aerial or transmitting circuit. ing to the inventionan additional circuit is coupled with the high frequency generatorand the aerial or transmitting circuit, which so untuned with relation of the carrier wave, and whose coupling with the generator .and the aerial is so adjusted that com-.

pensation or neutralization of the carrier frequency is realized in the transmitting circuit. Re erring to the drawing, I and II denote three-element electron discharge tubes of and an inductancel2 which Accord- The cathodes-are rendered incandescent by- A-batteries and the anode currents are supplied by B-batteries. In order to simplify the drawing neither the A-batt-eries nor the B-batteries have been shown.

v The speechfrequency to be transmitted is appl ed at terminalsl and 2. The trans former 3 conveys the speech potential tothe grid and filament of modulator tube I. The A modulator tube I is positioned in series with the grid andfilament of oscillator when and operates to vary the potential of the grid of tube II according to the speech frequencies."

' Oscillator tube-II is connected in any well- I tions. The arrangement shown in the drawto form a closed circuit with the inductance 14. The-antenna circuit is denoted by V and has in it an inductance 9 which is coupled to the inductance? by means of which coupling energy is transferred from the output circuit III to the-antenna circuit V. 'According to the invention, the antenna circuit V also has-in itan inductance '10 to which is coupled by means ofan inductance 11a neutralizing circuit IV. This circuit IV contains avariable condenser '13 for a. purpose hereinafter described more in detail, is coupled to the inductance 14. V v A The. operation of this arrangement is as follows: The tube II being connected :to. act

"as an oscillation generator will cause a current to flow 1n output circuit III of the 'de-' ing for producing sustained oscillations comprises an lnductance c011 14 havlng a portion invention, I claim ,thene be present in. circuit III and ivill be transferred into-the antenna circuit V by means of inductances 7 and 9, and 1nto the neutralizing circuit IVby means of induc- "tances '12 and 14:. Condenser 13, however, may be so adjusted that only for'energy at the carrier frequency will the phase relation be such that the carrier frequency energy Will be neutralized or partially neutralized in theantenna circuit V. For frequencies other than the carrier frequency the phase relations of the Voltages induced inantenna f circuit V Will be such that they will not be neutralized to any appreciable extent.

After theproper adjustment of phase and amplitude, the antennafc ircuit;V maybe said, to be uncoupled to the oscillator tube II with respect to the idle or carrier current.

i Itv is necessary that the circuit, IV should have as litt-ledan1ping possible in order that the modulated wa've may not be destroyed simultaneously with the suppression of the carrier Wave. 7 If the circuit is subject tobut l ttle damping, for frequencies 1 for fW'h lQli the condition of uncoupling is not satisfieId,[th-ere happens a. marked variation in the phase, and these oscillationsill be radiated Withasufficient intensity; 7

It is a good plan notto uncoupleycom- .pletely, that is, to choose an arrangement such that hennospeech modulation takes place, a. small current, sayhl0.% of the 'rr'laxiinuni current, will flow in the aerial. When the transmitting apparatus becomes I cycles.

Ha'v-zn described one embodiment of in 1. In combination, a: source of acarrier Wave ofv relatively high frequency, means for modulating said carrier Wave a relatively low frequency resulting in waves of carrier andrside-bandt frequencies, an antenna circuit, means coupling said antenna circuit to said source, and means permitting the transmissioniof a wave of said'si'de-band frequency and suppressing a Wave of'said carrier frequency comprising a tuned circurt coupled to said antenna circuit and to said source independently of the aforesaic coupling means. I a l 2. In combination, means for producing a carrier Ware, means for modulating said carrier Wave at an audible frequency, an

output circuit, a transmitting circuit coupled to said output circuit, a neutralizing circuit coupled to said transmitting circuit and to said output circuit in such manner that the transmitting circuit is substantially -un-' cc-upled from said output circuit with respect r to energyat the frequency of the carrier Wave.- f V e 3. Inconibination, anoscillation generator comprising an. electron discharge :tllbQWltll its grid and anode circuits coupled by'an inductance for the production of a'ica rrier Wave, means for modulating: said carrier Wave at an audible frequency resulting ,in

side-band and carrier frequencies, an output- V circuit which includes the inductance of said oscillation generator, a neutralizing circuit of: adjustable impedance" coupled to said inductance, a transmission circuit a coupled to said outputcircuit, and to said neutralizing circuit, and means .to adjusttheimpedanceof said neutralizingcircuit Whereby energy atsaid SlCl'GsbEiiIICl frequenciesm'ay betransrmttedwithout appreciable attenuation, Whilethe carrier frequencyener y may be suppressed; I 1

4. In combination, source carrier frequency energy, an an'te'nna'system, means totransfer from the source to the antenna system energy at the carrier and side band frequencies, andv means to transfer from the source to the antenna system energy at the carrier freq uency andof such phase relation that it will tend to neutralize the carrier W'ayeenergy inthe-antennasystein.

of modulated I 5; In combination, a. source of modulated carrier frequency energy, an antenna system 1 3 5 means to transferfron'i the" source to the antenna system energyat the carrier andside band frequ 'ncies, andmeans to transfer from: the source to the antenna systenr energy at the carrier frequency and of such phase relation that it will tend" to ALEXANDER M niseries.

tuned approximately to a side band fre-' neutralize the carrier Wave. energy in "the a antenna system. 

